typical timber construction details
TRANSCRIPT
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Typical timber construction detailsConnection Details to Be Avoided
Detail A1 - Glued laminated timbers, although relatively dry at the time of manufacture, may shrink as
they reach equilibrium moisture content in service. When fasteners are not located near the bearing seat
but in the upper portion of the beam, shrinkage in the beam over the depth, d, can cause the beam
reaction to be carried by the fasteners rather than in the bearing on the hanger. This induces notch shear
and tension perpendicular to grain stresses that can cause splitting along the beam as shown.
SUGGESTED REVISION
Seasoned embers. When supported members are
of seasoned material, the top of the supported
member may be set appro!imately flush with the
top of the supporting member.
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Detail A2 - This detail is similar to "etail #$ in
that shrinkage in the beam can result in the
bearing being carried by the fasteners rather
than the bearing on the hanger seat which, in
turn, results in notch shear and tension
perpendicular to grain stress. #lso, see "etail
#% concerning long rows of fastenersperpendicular to grain as it relates to the hanger-
to-girder connection. Section $.& discusses the
effect of end rotation on the fasteners in this
type of connection.
SUGGESTED REVISION
'nseasoned embers. When supported
members are of unseasoned material, the hangers
should be so dimensioned that the top edge of the
supported member is raised above the top of thesupporting member or the top of the hanger strap toallow for shrinkage as the members season in place.
(or supported members with moisture content at or
above fiber saturation point when installed, the
distance raised should be about )* of the member+s
depth above its bearing point.
Detail A3 - nd connections which include long
rows of
fasteners perpendicular to grain through steel
side members
should be avoided. Shrinkage of the wood will
be
restrained by the steel resulting in tension
perpendicular to
grain stresses. ecause the beam is not
supported by a
bearing plate, notch shear and tension
perpendicular tograin stresses at the end of the beam will also
result. The
individual or combined effect may cause
splitting of the
member.
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SUGGESTED REVISION
Seasoned embers. When supported members are
of seasoned material, the top of the supported
member may be set appro!imately flush with the
top of the supporting member.
Detail A4 - This detail is similar to "etail
#% e!cept that the beam is supported by
bolts through the plate located in a saw kerf
in the center beam.
SUGGESTED REVISION
artially /oncealed Type. (or moderate loads, base
may be let in flush with bottoms of purlins.
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Detail A5 - #n abrupt notch in the end of a
wood member creates two problems. 0ne is that
the effective shear strength of the member is
reduced because of the end notch. The other is
that the e!posure of end grain in the notch will
permit a more rapid migration of moisture in the
upper portion of the member. The individual orcombined effect may cause the indicated split.
SUGGESTED REVISION
/ommon eam Seat.
'sed to resist uplift and hori1ontal forces as well as
gravity loads. 2n the case of uplift, the notched beam
effect must be checked. The beam may be fastenedto the tabs with one or more bolts or, where forces
are greater, with bolts and shear plates.
Detail A6 - This condition is similar to that
shown in "etail #3. The shear strength of
the end of the member is reduced, tension
perpendicular to grain stresses are induced
and the e!posed end grain may result insplitting because of rapid drying.
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SUGGESTED REVISION
Sloped eam - 4ower end. The taper cut beam
should be in bearing contact with the bearing plate.
Detail A7 - This detail at the upper end of a
sloped beam is similar to the notched beam
detail shown in "etail #3.
SUGGESTED REVISION
Sloped eam - 'pper nd.
The support at the top end of a sloped membershould be designed with a sloping seat rather than a
notched end.
The bolt must be designed to resist the parallel-to-
grain component of the vertical beam reaction.
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Detail A8 - 2n this situation, the beam is bearing on the beam seat and the top is laterally supported by
clip angles or similar hardware. 2n a deep beam, the shrinkage due to drying reduces the depth of the
beam and will create a split at the upper connection. This connection will also resist deflection of the
beam, creating a hori1ontal reaction force that may cause damage to the wall or the beam.
SUGGESTED REVISION
4ateral support of the ends of beams
can be provided with clip angles anchored to the
wall but without a connection to the beam. This
will not restrain vertical movement due to end
rotation or beam shrinkage.
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Detail A9 - When a tension connection across a cantilever beam hanger is designed using integral tabs
either at the top or bottom of the hanger, splitting may occur due to shrinkage between the bearing
point of the hanger and the bolts as shown.
SUGGESTED REVISION
/antilever 5inge /onnection.
The vertical reaction of the
supported member is carried by the side platesand transferred in bearing perpendicular grainto the supporting member. The rotation due
to the eccentric loading is resisted by the bolts
through the tabs at the top and bottom. The
connector may be installed with the top 6and
bottom7 bearing plates dapped into the
members to obtain a flush surface or may be
installed without daps. 8otching on the
tension side should be minimi1ed.
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Detail A10 - This situation is similar to "etail #% where deep splice plates are applied to both faces of
the beam. This may be a splice over the column or a situation where one beam is supporting the ne!t
one. #s the wood shrinks, the steel side plates resist the shrinkage effect causing splits in the beams.
This condition is particularly ha1ardous if one beam is supporting the ne!t one as shown on the left oras a cantilever connection, because the splits at the bolt holes will reduce the effective strength of the
beam.
SUGGESTED REVISION
eams to Wood /olumn '-late. Welded steel
assembly passes under abutting wood beams
and is welded to steel side plate bolted to wood
column.
eam to Wood /olumn
T-lates. Steel T-plate is bolted to
abutting wood beams and to wood
column. 4oose bearing plate may be
used where column cross sectional area
is insufficient to provide bearing for
beams in compression perpendicular to
grain. eams should be checked for
notch shear with net uplift design.
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#rch oment Splice. "rawing
shows a typical moment splice. /ompression
stress is taken in bearing on the wood through a
steel compression plate. Tension is taken
across the splice by means of steel straps and
shear plates. Side plates and straps are used to
hold sides and tops of members in position.Shear is taken by shear plates in end grain.
Detail A11 - 4oads suspended from beams as
shown induce tension perpendicular to grain
stresses.
NOTE - This type of connection is to be used to
carry light loads only and must be designed by a
qualified design professional.
Suggete! Re"ii#$
4oads suspended from glued laminated timber
beams should be resisted from the top of the
member or at least above the neutral a!is.
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Detail A12 - This shows a general condition
where, particularly in continuous framing, the
top tension fibers have been cut to provide for a
recessed hardware connection or for the passage
of conduit or other elements over the top of the
beam. This is particularly serious in glulam
construction since the tension laminations arecritical to the proper performance of the
structure.
SUGGESTED REVISION
Welded and ent Strap 5anger. # separate
tension tie may be used across the top in lieu of the
tabs to resist lateral forces.
Detail A13 - Some designers try to conceal the
base of a column or an arch by placing concrete
around the connection. oisture will migrateinto the lower part of the wood and cause decay.
SUGGESTED REVISION
#rch Shoe with /oncealed #nchor olts.
/ounterbores are provided in arch base for anchorbolt pro9ections.
"o not place arch below finished concrete floor
level.
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Detail A14 - Similar to "etail #$% in that the
base of an arch or column is placed in a closed
steel bo! where moisture will accumulate and
cause decay.
SUGGESTED REVISION#rch #nchorage Where True 5inge 2s 8ot:equired. :ecommended for arches where a true
hinge is not required. ase shoe is anchored directly
to buttress. "o not embed arch in concrete floor.
Detail A15 - When the centerlines of membersdo not intersect at a common point in a truss,
considerable shear and moment stresses mayresult in the bottom chord. When these are
combined with the presumably high tension
stress in the member, failure may occur.
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SUGGESTED REVISION
onochord-Steel Straps. (or trusses
with continuous upper chord. rovide clearance
between web ends and chord. rovide shims at
web to prevent bending of straps.
Detail A16 - Truss chord to web connection
made from a single plate or plates welded
rigidly together.
8ot recommended when truss deflections could
produce rotation of members, which could
cause splitting.
SUGGESTED REVISIONSlotted Gusset lates. Slotted holes allow rotation
of 9oint, reducing tension perpendicular to grain
stresses.
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Detail A17 - Truss heel connection with
eccentric force lines that cause prying action
which may result in splitting of the members.
SUGGESTED REVISION
Truss 5eel /onnection. 2f substantial cross grain
shrinkage is anticipated, double steel strapsmay be used in place of single plate along bottom
chord.